Distillation process of monomers with the addition of an antifoam composition

ABSTRACT

An antifoam composition is disclosed which consists essentially of (1) 1 to 20 percent by weight of a silicone-glycol copolymer, (2) 65 to 98 percent by weight of a propylene glycol, and (3) 1 to 15 percent by weight of a hydrophilic silica which is preferably treated in situ. The composition is particularly useful in latexes.

United States Patent 11 1 Householder 1 Oct. 2, 1973 54] DISTILLATION PROCESS OF MONOMERS 3,634,288 1/1972 Youngs 252/351; WITH THE ADDITIQN OF AN ANTIFOAM 2,782,162 2/1957 Liddell 203/20 3,306,341 2/1967 Pugh et al 203/20 COMPOSITION Kermit W. Householder, Tonawanda, NY.

Inventor:

Assignee: Dow Corning Corporation, Midland,

Mich.

Filed: May 17, 1971 Appl. N0.: 144,263

References Cited UNITED STATES PATENTS 9/1968 Haluska 260/448.2 B

Primary Examiner-Wilbur L. Bascomb, Jr. AttorneyRobert F. Fleming, Jr., Laurence R. Hobey, Harry D. Dingman, Howard W. Hermann and Jack E. Moermond [57] ABSTRACT An antifoam composition is disclosed which consists essentially of (l) l to 20 percent by weight of a silicone-glycol copolymer, (2) 65 to 98 percent by weight ofa propylene glycol, and (3) l to 15 percent by weight of a hydrophilic silica which is preferably treated in situ. The composition is particularly useful in latexes.

6 Claims, N0 Drawings R is composed of ethylene radicals and radicals selected from the group consisting of propylene and butylene radicals, the amount of ethylene radicals relative to the other alkylene radicals being such that the ratio of carbon atoms to oxygen atoms in the total OR blocks ranges from 2.3:l to 2.821, 2 has an average value from to l00, and A is a capping group, (2) 65 to 98 percent by weight of polypropylene glycol having an average molecular weight in the range of 1,000 to 2,000, and (3) l to 15 percent by weight of a hydrophobic silica. I

The depression and/or suppression of foam in many systems is a problem. Each system is unique and requires its own antifoamer or defoamer. And while a particular composition may function well as an antifoam, it may at the same time introduce a new problem. The foregoing is true of latex systems.

It is an object of this invention to provide a new antifoam or defoaming composition which is particularly useful in latexes.

By way of example, during the preparation of styrene-butadiene latexes in emulsion the conversion of monomers to polymer is terminated at about 70 to 75 percent conversion as higher conversions yield polymers with inferior properties. The unreacted butadiene is generally removed by flashing at atmospheric and then reduced pressures. Finally, the unreacted styrene is removed by steam stripping (distilling) where foaming is a problem. Acrylonitrile-butadiene latexes are made by an analogous process. Other synthetic latexes also present similar foaming problems during preparation. Therefore, another object of this invention is to provide an antifoam composition which can be used in latexes, which composition significantly reduces the foaming problems during preparation.

Another object of this invention is to provide an antifoam composition which can be usedin latexes which composition does not cause fisheyeing when the latex is subsequently used in making coating compositions.

Yet another object is to provide an antifoam composition whose performance does not fade towards the end of processing.

Other objects and advantages of this invention will be apparent from the following description and examples.

The first component of the composition of this invention is a silicone-glycol copolymer having the general formula (CH SiO (CH SiO} I {(CH )GSiO ,,Si(CH In this copolymer the number of dimethylsiloxane units, as defined by x can range from 6 to 420. Preferably x has an average value of 50 to 100.

The number of methyl-glycol siloxane units in the copolymer is defined by y which can have an average value ranging from 3 to but which preferably falls in the range of 5 to 10.

The glycol portion of the copolymer is designated as G which is defined as a radical of the structure D- (OR),A. The glycol is attached to the silicon atom via alkylene radical D which preferably contains from one to 18 carbon atoms. Specific examples of D are the methylene, ethylene, propylene, isopropylene, butylene, octylene, decylene, octadecylene and myricylene radicals.

The (OR) portion of the glycol radical defines the alkylene oxide which constitutes the backbone of the glycol. It can consist of ethylene oxide units (R is an ethylene radical) and propylene oxide units (R is a propylene radical), ethylene oxide units and butylene oxide units (R is a butylene radical), or ethylene oxide units with propylene oxide units and butylene oxide units. However, the proportion of the ethylene oxide to the other alkylene oxides must be such that the ratio of carbon atoms to oxygen atoms in the total (OR) block ranges from 2.3:l to 2.8:]. The total number of )OR) groups is defined by 2 which has an average value from 10 to 100.

The A radical in the glycol portion of the copolymer is a capping group. By way ofillustration, the glycol can be hydroxy, acyl, ether or carbonate ester capped.

Preferably there is no more than a total of 15 atoms in The silicone-glycol copolymers described above are well known materials with some of them being commercially available. For those-unfamiliar with them attention is directed to U.S. Pat. No. 3,402,192 whose disclosure is incorporated by. reference. This patent sets forth typical methods of preparation and a more detailed description of these materials. v

The silicone-glycol can amountto l to 20 percent by weight of the total composition. It is preferable, however, that it be present in an amount ranging from 6 to 10 percent.

The second component of the composition of this invention is a propylene glycol. These glycols are also commercially available materials. It has been found that in addition to being propylene glycol, the molecular weight must be in the range of 1,000 to 2,000 with a molecular weight range of 1,000 to l,500 being perferred. The amount of this component can be from 6 5 to 98 percent by weight but is preferably in the range of to percent.

The third and last component of the composition of this invention is a hydrophobic silica.

A hydrophobic silica is one which has had its surface hydroxyl groups removed, generally by the reaction with an organofunctional silicone such as trimethylmethoxysilane, trimethylchlorosilane, hexamethyldisiloxane or hexamethyldisilazane. However, materials such as stearyltrichloride can also be used to treat the silica. The reaction or treatment of the silica with thesilicorie renders the silica hydrophobic as compared to its original hydrophilic nature. It has been found essential to obtain the best results in accordance with this invention that the silica be treated in situ; that is, the silica must be reactedwith the silicone or other treating agent during the preparation of the antifoam composition rather than being treated separately prior to the silica being admixed with the other components of the composition. 1

can be from 1 to 15 percent by weight but is preferably in the rangeof 6 to 10 percent.

The amount of the silica present in the composition The particular amount of the antifoam composition of this invention to be used for antifoaming purposes varies widely. Such factors as the type of product having the foam problem, the process involved, the equipment being used, and the extent to which one wishes to control the foaming determine the amount used. Thus it is difficult to set any meaningful numerical limitations as to the amount of antifoam composition to be employed. In practice, for example, anywhere from 5 parts of antifoam composition per million parts of composition being defoamed to 5 percent by weight of antifoam composition based on the weight of the composition being defoamed may be used with satisfactory results depening on the situation.

Now in order that those skilled in the art may better understand how the present invention can be practiced, the following examples are given by way of illustration and not by-way of limitation. All parts and percents referred to herein are on a weight basis unless otherwise specified.

1n the examples, performance of the antifoam compositions was evaluated by placing 300 ml. of unstripped latex in a 32 ounce bottle. The latex was then heated to 90C. by placing the bottle containing the latex in a boiling water bath. After 90C. was reached the antifoam composition was added to the latex and steam blown through the latex. Shortly after the steam is introduced the unreacted monomers begin to distill from the system causing foaming. A maximum foam height of less than 9 cm. is considered as passing the test.

After the latex has been stripped it was allowed to cool to room temperature. It was then filtered by passing it through 100 mesh and 325 mesh screens. The particles removed during filtration are preflock. Large amounts of preflock are undesirable.

A 0.003 inch thick film of the latex was cast on a clean glass plate. If less than five fisheyes were observed in a l-r inch X7 inch strip the antifoam composition passed the test.

EXAMPLE 1 An antifoam composition consisting essentially of about 4.2% of a silicone-glycol copolymer of the formula about 87.5% of propylene glycol having an average molecular weight of about 1,200 and about 8.3% of a pretreated hydrophobic silica was prepared as follows. 4% of hexamethyldisilazane and 8% of a non-hydrophobic silica (Quso G-30) were mixed together whereby the silica was treated and became hydrophobic. Then 84% of thepolypropylene glycol was added and mixed in and finally 4% of the silicone-glycol copolymer was mixed in and the product colloid milled at a setting of 10.

A second antifoam composition was prepared for purposes of comparison which was identical to the one above except that it contained none of the siliconeglycol copolymer and 88% of the polypropylene glycol was used in the preparation.

Both of the above antifoam compositions were evaluated by adding 1 cc. to a styrene-butadiene latex in the above-described test. The first composition, which represents this invention, gave good foam control. The second composition, made for purposes of comparison, gave good initial foam control but faded at the end of the test which was undesirable. Both compositions passed the preflock and fisheye tests.

EXAMPLE 2 An antifoam composition consisting essentially of about 8.3% of a silicone-glycol copolymer of Example 1, about 83.3% of propylene glycol having an average molecular weight of about 1,200 and about 8.3% of a hydrophobic silica treated in situ was prepared as follows. 4% hexamethyldisilazane and 40% of propylene glycol were mixed together and then added to 8% of a non-hydrophobic silica (Quso G-30) and mixed. Next another 40% of polypropylene glycol was mixed in and then the mixture heated at to 90C. while mixing.

Finally 8% of the above silicone-glycol copolymer was mixed and the product colloid milled at a setting of 15 mils.

A second antifoam composition identical to the one above was prepared as follows. 4% of hexamethyldisilazane and propylene glycol were mixed together. To this mixture 8% silica was added while mixing and heating at 75 to C. Then 8% of the silicone-glycol copolymer was mixed in and the product colloid milled at a setting of 15 mils.

Both of the above antifoam compositions were evaluated by adding 1 cc. to a styrene-butadiene latex in the above described test. Both compositions passed the test and were considered to be very good antifoams. The antifoam test was run for an extended time by adding styrene monomer to the latex as stripping was carried out. The first composition was run for one-half hour and the second composition for 1 hour. In both cases the antifoam composition failed only after the monomer was completely gone. Both compositions also passed the preflock and fisheye tests.

EXAMPLE 3 When the procedure of the preceding examples is carried out using acrylonitrile-butadiene rubber latexes, the antifoam compositions of this invention reduce the amount of foaming during the monomer stripping, and no preflock or fisheyeing problems are encountered.

EXAMPLE 4 When the antifoam compositions set forth below are substituted for the antifoam compositions of Examples l-3, there is a significant reduction in foaming, and no preflock or fisheyeing problems are encountered.

A. A composition consisting essentially of 1% of a silicone-glycol copolymer having the formula 98% of polypropylene glycol having a molecular weight of about 1,000, and 1% of a hdyrophobic silica treated in situ with trimethylchlorosilane.

B. A composition consisting essentially of 15% of a silicone-glycol copolymer having the formula (CILOaSiOl (CII3)2S10}100( olmsio hosuonm (0112M(OCzHOso(OCJHQmOCqIIg 75% of polypropylene glycol having a molecular weight of about 2,000, and of a hydrophobic silica treated in situ with stcaryl trichloride.

C. A composition consisting essentially of 20% of a silicone-glycol copolymer having the formula of about 1,500, and of a hydrophobic silica treated in situ with hexamethyldisiloxane.

That which is claimed is:

1. In a process of distilling unreacted monomers from a synthetic latex in which process foaming occurs, the improvement which comprises adding to the latex, prior to the distillation of the unreacted monomers therefrom, the antifoam composition which consists essentially of l. 1 to percent by weight of a silicone-glycol copolymer having the general formula wherein x has an average value from 6 to 420,

y has an average value from 3 to 30, and

G is a radical of the structure D(OR),A wherein D is an alkylene radical,

R is composed of ethylene radicals and radicals selected from the group consisting of propylene relative to the other alkylene radicals being such that the ratio of carbon atoms to oxygen atoms in the total OR blocks ranges from 2.3:1 to 2.8:],

z has an average value from to 100, and

A is a capping group,

2. 65 to 98 percent by weight of polypropylene glycol having an average molecular weight in the range of 1,000 to 2,000, and

3. 1 to 15 percent by weight of a hydrophobic silica whereby the foaming is significantly reduced.

2. The process of claim 1 wherein th latex is a styrene-butadiene latex.

3. The process of claim 1 wherein the latex is an acrylonitrile-butadiene latex.

4. In a process of distilling unreacted monomers from a synthetic latex in which process foaming occurs, the improvement which comprises adding to the latex, prior to the distillation of the unreacted monomers O CH 65% of polypropylene glycol having a molecular weight 10 wherein x has an average value from 50 to 100,

y has an average value from 5 to 10, and

G is a radical of the structure D(OR),A wherein D is an alkylene radical which contains from one to 18 carbon atoms,

R is composed of only ethylene and propylene radicals, the amount of ethylene radicals relative to the propylene radicals being such that the ratio of carbon atoms to oxygen atoms in the total OR blocks ranges from 2.3:1 to 28:1,

1 has an average value from 25 to 100, and

A is selected from the group consisting of hydroxy, acyl, ether, and carbonate ester capping groups,

2. to percent by weight of polypropylene glycol having an average molecular weight in the range of 1,000 to 1,500, and

3. 6 to 10 percent by weight of a hydrophobic silica, said hydrophobic silica having been treated in situ whereby the foaming is significantly reduced.

5. In a process of distilling unreacted monomers from a synthetic latex in which process foaming occurs, the improvement which comprises adding to the latex, prior to the distillation of the unreacted monomers therefrom, the antifoam composition which consists essentially of 1. 6 to 10 percent by weight of a silicone-glycol copolymer having the general formula (CH;) SiO( oH3 ,si01- 5 onnsi oklsuotfni o onmocsmmoo OH;

2. 75 to 90 percent by weight of a polypropylene glycol having an average molecular weight of about 1,200, and 3. 6 to 10 percent by weight of a hydrophobic silica treated in situ with hexamethyldisilazane whereby the foaming is significantly reduced.

6. The process of claim 5 wherein the latex is a styrene-butadiene latex.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,763,021

DATED October 2 1973 INVENTO (S) Kermit W. Householder It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 31, after the word "propylene" insert --and butylene radicals, the amount of ethylene radicals--.

Column 6, line 39, the formula should read,

(CH2)3(OC2H4),\,24(OC3H6),\J24OCCH3--.

Signed and Sealed this Eighth Day of February 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner nfParenls and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,763,021

DATED October 2 1973 INVENTO I Kermit W. Householder It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, line 31, after the word "propylene" insert --and butylene radicals, the amount of ethylene radicals.

Column 6, line 39, the formula should read,

--((}I-I SiO.[(CH SiO], [(CH )TiO], Si(CH O H (CH2)3(OC2H4),\/24(OC3H6),\/24OL|CH3'0 Signed and Scaled this Eighth Day of February 1977 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN 8 ff Commissioner uflatems and Trademarks 

2. The proceSs of claim 1 wherein th latex is a styrene-butadiene latex.
 2. 65 to 98 percent by weight of polypropylene glycol having an average molecular weight in the range of 1,000 to 2,000, and
 2. 75 to 90 percent by weight of a polypropylene glycol having an average molecular weight of about 1,200, and
 2. 75 to 90 percent by weight of polypropylene glycol having an average molecular weight in the range of 1,000 to 1,500, and
 3. 6 to 10 percent by weight of a hydrophobic silica, said hydrophobic silica having been treated in situ whereby the foaming is significantly reduced.
 3. The process of claim 1 wherein the latex is an acrylonitrile-butadiene latex.
 3. 6 to 10 percent by weight of a hydrophobic silica treated in situ with hexamethyldisilazane whereby the foaming is significantly reduced.
 3. 1 to 15 percent by weight of a hydrophobic silica whereby the foaming is significantly reduced.
 4. In a process of distilling unreacted monomers from a synthetic latex in which process foaming occurs, the improvement which comprises adding to the latex, prior to the distillation of the unreacted monomers therefrom, the antifoam composition which consists essentially of 6 to 10 percent by weight of a silicone-glycol copolymer having the general formula (CH3)3SiO((CH3)2SiO)x((CH3)GSiO)ySi(CH3)3 wherein x has an average value from 50 to 100, y has an average value from 5 to 10, and G is a radical of the structure -D(OR)zA wherein D is an alkylene radical which contains from one to 18 carbon atoms, R is composed of only ethylene and propylene radicals, the amount of ethylene radicals relative to the propylene radicals being such that the ratio of carbon atoms to oxygen atoms in the total OR blocks ranges from 2.3:1 to 2.8:1, z has an average value from 25 to 100, and A is selected from the group consisting of hydroxy, acyl, ether, and carbonate ester capping groups,
 5. In a process of distilling unreacted monomers from a synthetic latex in which process foaming occurs, the improvement which comprises adding to the latex, prior to the distillation of the unreacted monomers therefrom, the antifoam composition which consists essentially of
 6. The process of claim 5 wherein the latex is a styrene-butadiene latex. 